Why Are Balmer Absorption Lines Very Weak in the Spectra

question 187

Multiple Choice

Why are Balmer absorption lines very weak in the spectra of stars with low surface temperatures-significantly below 10,000 K, for example?

• A) The hydrogen atoms have to be hot enough to be ionized in order to show Balmer absorption.
• B) There is no emitted continuum radiation at Balmer-line wavelengths when the gas is so cool, so absorption will not be seen.
• C) Atoms need electrons that have been excited by high temperatures to the n = 2 level to undergo Balmer absorption.
• D) Hydrogen atoms have no electrons in any energy levels at these temperatures.